Gasoline manufacture



April 4, 1944. F. E, FREY 2,345,802

sAsoLINE MANUFACTURE Filed oct. 14. 1940 C) ff) BOLVNOILDVBJ POLYMERIZATION STlLL CATALYST POLYMERIZATION STILL HOLVNOILVHA OIL INVENTOR FREDERICK E. FREY TO NEY PROPANE Patented Apr. 4, 1944 PATENT OFFICE GASOLIN E MANUFACTURE Frederick E. Frey, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application October 14, 1940, Serial No. 361,138

5 Claims.

This invention relates to a process of manun facturing gasoline, and more particularly to the manufacture of gasoline from low boiling parailins especially from those having three and/or four carbon atoms per molecule. 5

The invention comprises, in combination, the following steps as one modification: subjecting parailins having three and four carbon atoms per molecule to at least one thermal conversion under conditions such as to produce hydrocarbons l boiling in the gasoline range, subjecting at least a part of the olefin and paraffinhydrocarbons effluent therefrom and having three and four carbon atoms per molecule to a conversion to effect olefin-parailin union forming hydrocarbons boiling l in the gasoline range, separating the gasoline thus formed, and recycling residual hydrocarbons having three and four carbon atoms per molecule to the thermal conversion.

An object of this invention is to provide a process of manufacturing gasoline from lighter hydrocarbons.

Another object is to utilize paraflins having three and four carbon atoms per molecule for the manufacture of gasoline.

Another object is to obtain a higher yield of gasoline from the oleflns having three and four` carbon atoms per molecule in the effluents from one or more thermal polymerization steps, in

which parafiins having three and four carbon atoms per molecule are cracked and polymerized to hydrocarbons boiling in the gasoline range, than can be obtained by virtue of recyling such olefins to the thermal conversion step or steps.

Other objects and advantages of the invention H5 will become obvious to those skilled in the art.

The invention will be readily understood from the following description and the accompanying drawing, which shows a flow-diagram for one preferred mode of operationl which is to serve as an example of my invention.

A three-carbon feed stock comprising chiefly propane enters the system through inlet l having control-valve 2. It is pumped, preferably as a liquid, by pump 3 and then is subjected to condi- 4 tions of thermal conversion, comprising cracking and polymerization, in tube-coil still. In this still, which is operated at a pressure of from '750 to 5000 or more pounds per square inch and a temperature of from 850 to 1200 F., the propane 50 is cracked Vto olefins, principally propylene and ethylene, which concommitantly undergo conversion into products of higher molecular weight, most of which boil in the gasoline range. The

products and unreacted propane pass to fraction` 55 ator 5, which serves to remove light gases; these light gases, which consists chiefly of hydrogen and methane and which may include some or all of the ethane and ethylene, are Withdrawn through valve 6 and outlet l. The hydrocarbons heavier than ethane pass through valve 8 and conduit 9 into fractioner I0, in which fractionation is effected into gasoline, which is withdrawn through valve Il and outlet i2, into oil boiling above the gasoline range, which is withdrawn through valve I 3 and outlet I4, and into a heavygas fraction comprising three-carbon and fourcarbon hydrocarbons, which passes through valve l5 and conduit IS into fractionator il. In fractionator Il three-carbon hydrocarbons are separated from four-carbon hydrocarbons; threecarbon hydrocarbons are recycled to the thermal polymerization step through valve I8 and conduit i9, and four-carbon hydrocarbons are passed through valve 20 andy conduit 2| to alkylator 22.

Occurring simultaneously with the foregoing steps are the following steps: A fourcarbon feed stock comprising chiefly either one or both of the butanes, enters the system through inlet 3l having control-valve 32. It is pumped, preferably as a liquid, by pump 33 and then is subjected to conditions of thermal conversion, comprising cracking and polymerization in tube-coil still 34. In this still, which is operated at a pressure of from 750 to 5000 or more pounds per square inch and a temperature of from 850 to 1200 F., the butanes are cracked to olens, principally butylenes, propylene, and ethylene, which concomitantly unn dergo conversion into products of higher molecular weight, most of which boil in the gasoline range. The products and unreacted butanes pass to fractionator 35, which serves to remove light gases; these light gases, which consists chiefly of hydrogen and methane and which may include some or all of the ethane and ethylene are withdrawn through valve 36 and outlet 3l. Hydrocarbons heavier than ethane pass through conduit 38 and valve 39 into fractionator 40, in which fractionation is effected into gasoline, which is withdrawn through valve 4l and outlet 42, into oil boiling above the gasoline range, which is withdrawn through valve 43.and outlet t4, and into a heavy-gas fraction comprising three-carbon and four-carbon hydrocarbons, which passes through valve 45 and conduit 46 into fractionator 41. In fractionator 5l four-carbon hydrocarbons are separated from three-carbon hydrocarbons; fourcar'oon hydrocarbons are recycled to the thermal polymerization step through valve 48 and conduit 49, and three-carbon hydrocarbons are passed through valve 50 and conduits 5| and 2| to alkylator 22.

If desired, part of all of the three-carbon and four-carbon hydrocarbons from fractionator I9 may be passed through Valve 23 and conduits 24 and 2| directly to alkylator 22 without going to fractionator |1.. Similarly, part or all of the three-carbon and four-carbon hydrocarbons from fractionator 40 may be passed through valve 53 and conduits 54 and 2| directly to alkylator 22 without going to fractionator .41. Also, if desired, part or all of the three-carbon hydrocarbons from fractionator 41 may be passed through valve 25 and conduit 26 to conduit I9, which then conveys them to the propane thermal polymerization still 4. Considerable control of the composition of the material passing through conduit 2| into alkylator 22 thus may be effected by varying the relative amounts of the streams that pass through valves I5., 23, 25, 45, 50, and/or 53. Moreover, additional advantageous control of the composition of the material passing through conduit 2| into alkylator 22 may be effected by operating fractionator 41 in such a manner that part or if desired, substantially all of the isobutane passes with the three-carbon hydrocarbons through valve 50 and conduits 5| and 2| into alkylator 22, and the normal butane and the residual isobutane, if any, are recycled through conduit 49, as already explained, to the thermal polymerizatin step; or, if desired, fractionator 41 may be so operated that substantially pure isobutane passes through valve 50, and the threecarbon hydrocarbons are passed substantially entirely through valve 25.

The thermal conversion stills 4' and 34 generally are operated at a pressure of from 1500 to 3000 pounds per square inch, but pressures somewhat outside this range,.from as low as about 750 pounds per square inch to as high as about 5000 pounds per square inch, or more, may be used; a pressure of about 2500 pounds per square inch is preferred. 'I'he stills generally are operated at a temperature of from 900 to 1150 F., but temperatures somewhat outside this range, from as low as about 850 F. to as high as about 1200* F., may be used; a temperature of about 1070 F. is preferred for the propane still 4 and one of about 1020 F. for the butane still 34. At these preferred temperatures, the reaction time is of the order of 1 to 2 minutes, although at the same temperatures longer reaction times will be used to convert propane in still 4 than will be used to convert butane in still 34. For example, for n-butane at 1020 F. and 2500 pounds per square inch, an optimum reaction time is about 1.8 minutes, and for propane at the same temperature and pressure an optimum reaction time is about 10 minutes.

In alkylator 22, the hydrocarbons brought thereinto by conduit 2| are treated to effect union of low boiling isoparaflinssuch as isobutane with oleiins having three and four carbon atoms' to the molecule to form isoparains predominantly of seven and eight carbon atoms. which are desirable ingredients of gasoline. A minor proportion of the olefins appear to undergo polymerization, especially if the concentration of low boiling isoparailns is not considerably in excessof that of the olens, and some other side-reactions also .appear to-occur to small extents. 'Ihe conditions in alkylator 22 maybe those of a noncatalytic alkylation process, but preferably are those of an alkylation process using a catalyst such as an aluminum halide catalyst including aluminum chloride or bromide, and alkali metal haloaluminates such as sodium chloroaluminate, or zinc chloride or bromide, boron fluoride, or zirconium tetrachloride or the like, or concentrated sulfuric acid, or concentrated hydroiluoric acid, or the like, as for example the process disclosed in the copending application of Frey et al., Serial No. 87,790, issued February 25, 1941, as U. S. Patent No. 2,233,363 or in my copending application -Serial No. 315,063, now Patent 2,322,800, issued June 29, 1943.

If a catalytic alkylation process involving a liquid or a mobile catalyst is used, the catalyst may be fed into alkylator 22 through inlet 55 having control-valve 56. In such a process, it is advantageous to use sulfuric acid or hydrofluoric acid as the catalyst, especially if the initial fourcarbon feed stock comprises isobutane, as these catalysts appear to be more selective than other known alkylation catalysts for the alkylation of isoparans. When sulfuric acid is used as a catalyst, it should have a strength between about 90 and 105 per cent, advantageously from 96 to 102 per cent. To minimize concurrent polymerization. reactions, the mixture of hydrocarbons and sulfuric acid in alkylator 22 must be agitated vigorously, and the concentration of olens preferably should be kept low relative to the concentration of isobutane. The reaction temperature should be kept between 0 and 125 F., preferably at about 30 to '10 F. Hydrofluoric acid should have a concentration greater than 90 per cent, and may in some cases be substantially anhydrous, although this is not always necessary.

If desired, hydrocarbon fractions comprising substantial amounts of isoparans such as isobutane, isopentane, or isohexanes may be fed to alkylator 22, as through inlet having controlvalve 8|, for the purposes of increasing the yield` of gasoline produced in alkylator 22 and of decreasing the volatility of such light-gasoline fractions, or as substantially the sole material to be reacted with the propylene and butenes passed to this step.

After substantially all of the oleflns have undergone reaction in alkylator 22 into heavier hydrocarbons boiling principally in the gasoline range, the mixture of hydrocarbons and mobile alkylation catalyst is passed through valve 51 and conduit 58 to separator 59, in which the hydrocarbons'and the alkylation catalyst are separated, as by settling into two layers, followed if desired byan alkali treatment of the hydrocarbon layer to remove acidic or other nonhydrocarbon material.

The alkylation catalyst may be withdrawn through valve 60 and outlet 6|, and thence it may be subjected to a process of reclamation, if desired; or, alternatively, it may be returned, partly'or entirely, as is desired or as appears best, to alkylator 22through valve 62 and conduit 63. The hydrocarbons after being freed from the alkylation catalyst -in separator 59, are passed through valves 64 and 65 and conduit 66 to fractionator 61, in which fractionation is effected into a gasoline fraction, which is withthrown through valve 68 and outlet 69, into an oil fraction, which is withdrawn through valve 10 and outlet 1|, and into one or two (as desired) light-hydrocarbon fractions comprising chieily propane and butanes, which are conveyed t0 one or both of the. thermal polymerization:

stills 4 and 34 through conduits 12 and 13, in proportions controlled by valves 14 and 15.

If a fixed or immobile alkylation catalyst is used, separator 59, inlet 55, valve 56, and the conduits and valves contiguous to separator 59 may be isolated or omitted, and the hydrocarbon effluent from alkylator 22 may be passed directly to fractionator 61 through valves 16 and B5 and conduit 66.

In a modification of the process, part or all oi the hydrocarbon eluent' from separator 59 is passed through conduit 11 to either one or both of the fractionators I and 40, n proportions controlled by valves 18 and 19. In fractionator lil and/or 40, the gasoline is removed, and thence the paralns having three and four carbon atoms per molecule are further processed in any of the Ways elsewhere herein described. Similarly, if separator 59 is not used, part or all of the hydrocarbon effluent from alkylator 22 may be passed through conduit 11 to one or both of the fractionators i0 and 40. If all of the hydrocarbon material passing through valve 64 and/or valve 16 is passed through conduit 11, fractlonator 61 and its contiguous conduits and valves advantageously may be omitted, at some saving of investment cost,

It is to be understood, of course, that various operating units have been shown diagrammatically, such as the thermal conversion, or' polymerization, stills and the fractionators, the alkylator, and the like, and that Various pumps, cooling towers, reflux accumulators and surge tanks, furnaces and the like are to be included in any commercial plant. The details of such supplementary equipment will be' somewhat different and unique for each particular modiiication, and can be readily designed and supplied for any particular case -by one skilled in the art, in the light of the present disclosure.

In some situations in which the investment cost must be kept low, one thermal conversion still may be used for cracking and polymerizing a feed stock comprising mainly propane and one or both butanes, although the gasoline produced is not so advantageous in quantity and in quality as those produced by the use of separate stills for three-carbon and for four-carbon hydrocarbons. The investment cost of the second thermal polymerization still 34 and its accompanying pump 33 and fractionators'35, 40 and 41 thus is eliminated. In the operation of such a simpliiled system, the stock comprising both propane and butane, preferably with one or the other in substantial excess, is processed substantially in the manner already described for propane alone, or 4butane alone, but the fraction of three-carbon and four-carbon hydrocarbons from fractionator I0 preferably is sent through valve 23 and conduits 24 and 2| directly into alkylator 22, whereupon fractionator I1 and its accompanying conduits and valves may be omitted atsome additional saving of investment cost. The resultant simplified combination of thermal conversion and the alkylation steps has the advantage over the thermal conversion step alone in that the olens having three and four carbon atoms per molecule in the effluent from the thermal conversion stepare utilized to produce, by alkylation, a gasoline higher in quantity and in qualiti. than that which would be' produced from the same oleilns if recycled to the thermal conversion step. With such a modification it is generally preferable to use as the alkylation catalyst a material such as aluminum chloride or bromide, or a suitable metal haloaluminate. The alkylation gasoline may be stabilized along with the thermal product to produce a single product from the combined steps, the appropriate gaseous eilluent of the alkylation being passedto the thermal conversion, as previously discussed.

The following further examples are given to illustrate a few of the many possible modes of operation; they are not to be taken as establishing limitations of the invention.

Example I A three-carbon feed stock comprising chiefly propane is subjected to concurrent unitary thermal cracking and polymerization at a pressure of 2500 pounds per square inch in-a tube-coil at a temperature of about 1070o F. for a soaking time of about 1.8 minutes. The effluent from the cracking-polymerization coil is passed into fractional-distillation equipment, wherein it is separated into a lightgas fraction, a three-carbon fraction, a four-carbon fraction, a gasoline fraction, and a tar or heavy-oil fraction, The lightgas fraction. which amounts to about 17 per cent by Weight of the effluent and consists chiefly oi methane and ethane together with some hydrogen, is withdrawn from the system. The threecarbon fraction, which amounts to about 67 per cent of the eflluent and consists chiey of propane, is recycled to the thermal polymerization step. The four-carbon fraction, which amounts to about 5` per cent of the effluent and has high contents of isobutane and isobutylene that result from complex reactions not well understood but beneficial for my purpose, is passed into a sulfuric-acid alkylator. The gasoline and tar fractions, which amount to almost 11 and less than l per cent of the eilluent, respectively, are withdrawn from the system.

Simultaneously a four-carbon feed stock comprising chiefly isobutane is subjected to concurrent thermal cracking and polymerization at a pressure of 2500 pounds per square inch in another tube-coil at a temperature of about 1020o F. for a soaking time of about 4 minutes. The effluent from the tube-coil is passed into fractional-distillation equipment, wherein it is separated into a light-gas fraction, a three-carbon fraction, a four-carbon fraction, a gasoline fraction, and a tar or heavy-oil fraction. The light-- gas fraction, which amounts to about 14 per cent by weight of the eilluent and consists chiefly of methane and ethane, is withdrawn from the system. The three-carbon fraction, which amounts to about 1l per cent of the effluent and contains 82 per cent of propane, is passed to the propane thermal cracking-polymerization tube-coil. The four-carbon fraction. which amounts to about 60 per cent o1 the effluent and consists chiefly. of isobutane with a small olefin content, is passed to the sulfuric-acid alkylator already mentioned. The gasoline and tar fractions, which amount to about 13 and 2 per cent of the effluent, respectively, are withdrawn from the system.

In the sulfuric acid alkylator, the combined four-carbon hydrocarbon fractions are subjected to the action of sulfuric acid having a strength of 96 to 102 per cent and' at a temperature of about 70 F. After the hydrocarbon material has become substantially olefin-free, it is separated from the acid by settling of the acid-hydrocarbon mixture into two layers; the' upper or loydrocarbon layer is passed into fractional-distillation equipment, wherein the hydrocarbons are separated into a butane fraction, which is returned to the "butane thermal cracking-polymerization coil, and into gasoline and tar fractions, which are withdrawn from the system. The gasoline, which is about equal in amount; to that produced by the propane thermal cracking-polymeriaation unit, is principally isoparainic and has an excellent antilrnock rating.

Eixample II A three-carbon feed stock comprising chiefly propane is processed as in Example I, with a separation of the effluent as v.lescribed Simulteneously. a butane fraction comprising about 35 per cent isobutane and 65 per cent normal butane is subjected to concurrent thermal cracking and polymerization at a pressure of 2500 pounds per square inch in a tube-coil at about 1020 F. for a soaking time of about 2.5 minutes. The effluent is fractionally distilled into a light-gas fraction, a (3s-C4 fraction, a C4 fraction, a gasoline fraction, and a tar or heavy-oil fraction. The light-gas fraction, which amounts to about 16 per cent by Weight of the efliuent and consists chiefly ci methane and ethane, is withdrawn from the system. The C3-C4 fraction, which amounts to about 20 per cent of the eiiluent and contains principally propylene, and isobutane, with minor amounts of propane, butylene. and normal butane, is passed to an alkylator, along with the four-carbon fraction from the efliuent of the propane conversion. The C4 fraction, of which over 75 per cent is normal butane, with some butylenes and a little isobutane, is recycled back to the butane thermal cracking-polymerization step. The gasoline and tar fractions, which amount to about 1G and 2 per cent of the eflluent, respectively, are Withdrawn from the system.

In the alkylator the three-carbon and fourcarbon hydrocarbons are subjected to the action of concentrated hydrofluoric acid at about '70 F. After the hydrocarbon material has become substantially olen-free, it is separated from the acid by settling of the acid-hydrocarbon mixture into two layers. The upper or hydrocarbon layer is removed and fractionally distilled into a threecarbon fraction. which is passed to the propane thermal cracking-polymerization still, into a four-carbon fraction, which is passed to the butane thermal cracking-polymerization still, and into gasoline and tar fractions, which are withdrawn from the system. The gasoline, which is somewhat greater in amount than that produced by the butane thermal cracking-polymerization unit, is principally isoparaffinic and of good :antiknock rating.

As a modification of the process illustrated by this example, sufficient isobutane for the alkylation step can be isolated from the butane charge before the thermal cracking-polymerization step. In such a case, substantially all the C4 hydrocarbons in the eiiiuent are recycled, and only a small C3 fraction, having a high content of propylene, is sent from this effluent to the acid alkylation 4 step. The isobutane separated from the butane Example III A feed stock comprising chiefly propane is processed as in Example I. Simultaneously, a feed stock comprising chiefly isobutane is also processed as in Example I except that the threecarbon hydrocarbons and only about half of the isobutane in the effluent from the butane thermal cracking-polymerization tube-coil are sent to the sulfuric-acid alkylator instead of all the fourcarbon hydrocarbons; the remainder of the isobutane and the other four-carbon hydrocarbons are recycled to the butane cracking-polymerization tube-coil. The fraction sent to the alkylator amounts to 39 per cent of the efiiuent from the butane tube-coil and contains about 5 per cent propylene` and 72 per cent isobutane, with some propane and isobutylene, The four-carbon fraction recycled to the cracking coilamounts to 32 per cent of the effluent. In the alkylator the hydrocarbons in the fraction just described and the four-carbon hydrocarbons from the propane cracking-polymerization tube-coil are subjected to the action of sulfuric acid at a strength of 96 to 102 per cent and at a temperature of about 70 F. The yield of gasoline from the alkylator is somewhat less than the yield of gasoline from the propane cracking-polymerization tube-coil and is chiefly isoparafnic and has an excellent octane rating.

Example IV A propane-butane stream from a natural gasoline plant was charged to a unitary thermal conversion unit, operated at a discharge pressure of 1400 pounds per square inch with an initial heating period and an immediately following conversion period which gradually increased to a maximum of 1085" F., for a total heating and reaction time of about 5 minutes. From the eiiluent are separated light gases which are discharged from the system, a pentane and heavier fraction from which a gasoline stock is recovered, and a recycle butane fraction. The original butane stream and the recycle stream have the following compositions, in per cent by weight.

Charge Recycle Per cent Per cent 0. 44 2. 33 0. 94 8. 10 1.03 10.17 20. 08 8. 66 87. 42 49. 80 i Butylenes 8.71 Pantano and heavier 1.03 i. 29

Unsaturates 18. 40

hydrocarbon portion of the eiiiuent, after separation from the catalyst, is Washed ywith alkaliand subjected to a simple distillation into a C4 and lighter fraction and a C5 and heavier fraction.

The light fraction, of which the olen content is now less than is passed to the thermal con version unit in admixture with fresh butane charge. The C5 and heavier fraction, comprising predominantly paraillnic Cu to Cio hydrocarbons of low volatility, is admixed with the corresponding product of the thermal conversion unit, the entire gasoline product of the combined process being stabilized and cut to a 400 F. end point together. On a butane-Iree basis. the yield per pass of the thermal conversion unit with straight recycle and a reaction time of about 4 minutes, less time being required because of the higher olefin content of the recycle. is 13.2% by weight,while when combined with treatment of the recycle as described the total yield per pass is increased to about 38%, the composition of the thermal conversion etlluent being about the same, although with an in creased eiiiciency of conversion of C: hydrocarbons. The total gasoline available from the combination process is increased about above that of the increase due to the Cs and heavier fraction from the catalytic alkylation, since this product is appreciably less volatile than the corresponding product of the thermal conversion unit, and a balanced gasoline containing both products can contain an increased amount of butane.

In the foregoing examples, the yield of gasoline obtained from the olens sent to the alkylator from the thermal conversion steps is about twice that which would be obtained from these oleiins if they were recycled to the thermal conversion steps.

The gasolines obtained from the propane thermal conversion still, from the butane thermal conversion still, and from the alkylator may be used as such separately, or they may be blended together in any desired proportions to produce one or more motor fuels having any desired vapor pressure, volatility, distillation curve, and knock rating.

As many modifications of the invention will be obvious to those skilled in the art, the invention should not be limited unduly by the foregoing atoms per molecule to the rst thermal conversion, recycling normal butane eiiluent from the second thermal conversion back to the said second thermal conversion, passing hydrocarbons eiliuent from the ilrst thermal conversion and having four carbon atoms per molecule and hydrocarbons effluent from the second thermal conversion and having four carbon atoms per molecule and substantially freed from normal butane to a catalytic alkylation to effect olefin-parailln union forming parailinic hydrocarbons boiling in the gasoline range, separating and removing gasoline-range and higher-boiling 'products thus formed, passing residual hydrocarbons having three carbon atoms per molecule to the said first thermal conversion, and passing residual hydrocarbonsl having four carbon atoms per molecule to the second thermal conversionV 2. 'I'he process of claim l, in winch the alkylation catalyst is concentrated hydrofluoric acid.

3. The process of claim 1, in which the alkylation catalyst is concentrated sulfuric acid.

4. The process of claim 1, in which the alkylation catalyst is an aluminum halide.

5. The process of claim l, in which the alkylation catalyst is aluminum chloride.

FREDERICK E. FREY. 

